The present invention generally relates to electrophotography and more particularly, to a developing apparatus for supplying developing material onto the surface of a photoreceptor in a developing process of an electrophotographic copying machine and the like.
For feeding developing material onto the surface Pa of a photoreceptor P in the form, for example, of a drum endless belt or the like, there has conventionally been employed a developing apparatus D as shown in FIG. 1, which includes a developing sleeve or magnet roller Rm rotatably provided in a housing Dh so as to be partially exposed through an opening Da of the housing Dh to confront the photoreceptor P, and a stirring roller Rs also rotatably disposed in the housing Dh in which the developing material m is accommodated. The magnet roller Rm made of a hollow pipe of an electrically insulative material includes therein a main pole magnet M1 having one magnetic pole thereof directed outwardly, and interpole magnets M2 each having its magnetic pole opposite in polarity to that of the above one magnetic pole of the main pole magnet M1, directed outwardly. Upon rotation of the stirring roller Rs, the developing material m is subjected to triboelectric charging so as to be attracted onto the surface of the magnet roller Rm by the magnetic induction of the magnets M1 and M2 disposed therein. For stably supplying the developing material m onto the surface Pa of the photoreceptor P, it is necessary to restrict or limit the amount of the developing material m to be attracted onto the surface of the magnet roller Rm to a predetermined rate, and for this purpose, a doctor blade B is provided adjacent to the lower portion of the magnet roller Rm. Thus, by the attraction of the developing material m onto the surface of the magnet roller Rm (referred to as brush bristle formation hereinafter), the developing material is supplied onto the surface Pa of the photoreceptor P as the magnet roller Rm rotates.
In the conventional developing apparatus as described so far, however, there has been such a disadvantage that, since the magnetic brush bristles of the developing material thus formed are directed upwardly and downwardly with respect to the central position of the main pole magnet M1 of the magnet roller Rm, faulty bristle formation tends to take place in the vicinity of the central portion of the main pole magnet, and it becomes impossible to stably supply a sufficient amount of developing material onto the photoreceptor surface, thus resulting in a deteriorating quality of the copied images. There has also been such an inconvenience that the developing material not attracted onto the photoreceptor surface Pa adheres to the surface of the doctor blade B to give rise to faulty bristle formation, or such developing material falls onto copy paper sheets to obstruct formation of copied images in good quality.
Meanwhile, the developing material as described so far may be broadly divided into a mono-component developing material employing toner of a magnetic material, and a dual-component developing material composed of toner of thermoplastic resin powder and magnetic carrier. In the dual-componoent developing material as referred to above, the toner and carrier having different charging tendencies are stirred by the stirring roller Rs so as to be charged respectively into different polarities by triboelectric charging. Through selection of raw materials for the above toner and carrier by taking into account the frictional order in the charging tendency, the toner is charged in a polarity opposite to that of the charge imparted to the surface Pa of the photoreceptor P, and thus, in the developing process, only the toner is attracted onto the surface Pa of the photoreceptor P. In the conventional developing apparatus, however, since the doctor blade B for restricting the bristle formation by the developing material on the surface of the magnet roller Rm is made of a non-magnetic material, the carrier charged to the same polarity as that on the photoreceptor surface Pa tends to fall of the magnet roller Rm during supply of the toner in the developing process to adhere onto the surface of the doctor blade B, and such carrier adhering onto the doctor blade surface is increased with the increase in the number of copying operations and falls down spontaneously or by the vibration of the copying machine, etc., thereby soiling the interior of the machine or copy paper sheets, or obstructing formation of copied images in good quality.